This project entails continuing analyses of data derived from a large- scale, placebo-controlled field trial of B subunit-killed whole cell (BS- WC) and killed whole cell-only (WC) oral vaccines against cholera, conducted between 1985-90 in the Matlab field studies area of the International Center for Diarrheal Disease Research, Bangladesh. The trial enrolled ca. 89,000 subjects for study. Analyses of the first three years of follow-up revealed that each vaccine conferred ca. 50% protection against cholera episodes detected among patients seeking care at medical facilities. Additional work is ongoing to determine whether antecedent infection by Helicobacter pylori, a known cause of persistent hypochlorhydria, is a risk factor for cholera in Bangladesh. This study is evaluating serological evidence of H. pylori infection in cholera cases and community controls assembled during the field trial.